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THE VELOCITY FIELD IN THE NEAR WAKE OF A FREELY-OSCILLATING CIRCULAR CYLINDER AT LOCK-IN

Gregory A. Kopp
Boundary Layer Wind Tunnel Laboratory and Advanced Fluid Mechanics Research Group Faculty of Engineering Science, University of Western Ontario, London Ontario, N6A 5B9 Canada

Salim Fathi
Boundary Layer Wind Tunnel Laboratory Faculty of Engineering, University of Western Ontario London, Ontario, N6A 5B9, Canada

Brian Havel
Advanced Fluid Mechanics Research Group Department of Mechanical and Materials Engineering Faculty of Engineering, University of Western Ontario London, Ontario, N6A 5B9, Canada

Robert J. Martinuzzi
Department of Mechanical and Manufacturing Engineering Schulich School of Engineering, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4

Jon Galsworthy
Boundary Layer Wind Tunnel Laboratory Faculty of Engineering, University of Western Ontario London, Ontario, N6A 5B9, Canada

Resumo

Two-component velocity measurements were made with laser Doppler velocimetry in the near wake of a freely vibrating, elastically mounted, light weight circular cylinder at lock-in. Maximum cylinder displacements of 0.75d were observed for a mechanical damping level of about 0.2% of critical. The Scruton number was 1.5, while the Reynolds number at lock-in was about 53,000. The velocity data were phase averaged relative to the periodic loading cycle. Significant differences in the details of the turbulence when the cylinder is oscillating compared to the stationary case were observed. These differences lead to increased production of incoherent turbulence. Interestingly, the wake of the oscillating cylinder is narrower than that for the stationary cylinder, so that less engulfment has occurred in spite of the increased strength of the main vortices. This is attributed to the reduced three-dimensionality during formation, in particular, the mitigation of oblique shedding and vortex dislocations.